The present invention relates to an automatic writing instrument which is constructed to feed the writing lead into writing position merely through application of pressure or thrust against the writing point end of the pencil, or against the writing tip of the lead itself. More particularly, the present invention relates to a mechanical pencil of the type described above in which a slider having a lead retainer and a projectable tube is urged rearwardly through the application of pressure against the writing point end against a resilient force of a spring device mounted within a pencil casing together with the lead in the tube, and the lead is advanced from the writing end of the tube for a predetermined distance after the pressure or thrust is released.
U.S. Pat. No. 2,865,330 to E. V. Swank shows a similar type of the writing instrument which is constructed to both feed and retract the writing lead into and out of writing position through application of thrust against the writing point end of the pencil, or against the writing tip of the lead. In the known writing instrument, a sleeve for clamping a lead engaging collet chuck is designed to be held or suspended temporarily when the writing point end, i.e., a slidable tube or the writing tip of the lead, is pressed by the application of the thrust. When the thrust is released, the lead in the lead engaging collet chuck is advanced, and then the temporary suspension of the collet chuck is released to advance the sleeve so that the lead is advanced from the writing point of the sleeve. However, the pencil disclosed in the above-described U.S. Pat. No. 2,865,330 incorporates a comparatively complex device for temporarily holding the lead engaging collet chuck.
Japanese Patent Application No. 53-77570 published under publication No. 54-14823 on Feb. 3, 1979 shows a similar type of pencil, in which a tubular writing point and a lead retainer are caused to slide or be retracted through application of a pressure against the writing point with a lead engaging collet chuck being held still. In the pencil, when the pressure on the tubular writing point is released to permit the tubular writing point to advance to the former position, the lead engaged by the lead retainer can be advanced to the end of the tubular writing point, while, however, the lead is not advanced any further from the very end of the tubular writing point since the lead engaging collet chuck is not designed to retract by the application of a pressure against the tubular writing point. In order to advance the lead so as to cause it to project from the end of the writing point in writing position, a push-button or similar manually actuated controls must be actuated.
Another structure of the similar type of the writing instrument is shown in Jananese Utility Model Application No. 51-141854 published under Publication No. 55-5350 on Feb. 7, 1980 in which the writing instrument incorporates, for the purpose of retaining a tubular writing point at a predetermined projected position, a sleeve frictionally engaged with a tubular slider such that the frictional resistance force therebetween is designed to be greater than the frictional resistance force between the lead and the lead engaging collet chuck. However, the lead projection must be conducted by actuation of a push-button.